The present invention relates to a process for producing an electronic part such as LSI (large-scale integrated circuit), multilayered wiring substrates, etc., and the electronic part produced by the process.
Cross-sectional view of a conventional multilayered wiring substrate for high density application, provided on a main substrate with a thin film multilayered wiring comprising an organic insulating film and a metallic wiring pattern is shown in FIG. 11, where the multilayered wiring substrate has pads 3 for wiring extension on the front side of a ceramic substrate 2 and pads 4 for external connection on the back side thereof, each formed at the corresponding positions by printing patterns of, for example, tungsten paste, and these pads 3 and 4 at the corresponding positions are electrically connected to one another by sintered metallizing of printing patterns of the same tungsten paste, formed through the ceramic substrate 2 from the front side to the back side.
These printing patterns of tungsten have a poor bondability to a metallic wiring pattern of aluminum or the like provided on the substrate 2 or to a solder for use in external connection, for example, connection to a mother board. In order to improve the bondability to the metallic wiring pattern or solder, nickel plating layers 5 and 6 are formed on the pads 3 for wiring extension and the pads 4 for external connection, respectively.
When the nickel plating layer 5 is directly connected to the aluminum wiring pattern 10 as an upper layer, nickel and aluminum undergo a thermal reaction on the contact surface between the nickel plating layer 5 and the aluminum wiring pattern 10 during the heat treatment for forming an organic insulating film 9, and as a result a fusion layer of nickel and aluminum is formed at the contact surface. The fusion layer is so low in the electroconductivity that the electroconductivity between the nickel plating layer 5 and the aluminum wiring pattern 10 is lowered. In order to prevent formation of the fusion layer, a chromium film layer 8 is formed on the nickel plating layer 5 as an upper barrier metal layer. That is, the aluminum wiring pattern 10 is connected to the nickel plating layer 5 through the chromium film layer 8 in respective contact holes provided in the organic insulating film 9.
In a multilayered wiring substrate provided with two metallic wiring films of different materials on pads for wiring extension, these metallic wiring films have been usually formed in the following manner.
At first, a metallic wiring film is formed on the pads for wiring extension as a lower layer and patterned. Then, another metallic wiring film is formed as an upper layer directly on the lower layer, and patterned by an etching agent capable of selectively etching only the upper layer metallic wiring film among the lower and upper layer metallic wiring films.
When a photolithographic technique is used for patterning the upper layer metallic wiring film, the photoresist used for the patterning is released from the upper layer metallic wiring film by a resist-releasing agent after the patterning.
This kind of the foregoing technique is disclosed, for example, in JP-A-62-36868.
In the foregoing technique the lower layer metallic wiring film has been sometimes etched by the etching agent for patterning the upper layer metallic wiring film or corroded or deteriorated by the resist-releasing agent for removing the patterning photoresist. Consequently, when an organic insulating layer is further formed on the metallic wiring films in the multilayer structure, there have been such inconveniences as a decrease in the interlayer bondability between the exposed lower layer metallic wiring film and the organic insulating film, formation of clearances at the interface between the lower layer metallic wiring film and the organic insulating film, etc.
To prevent these inconveniences, it has been required to select an etching agent capable of selectively etching only the upper layer metallic wiring film and incapable of etching the lower layer metallic wiring film among the upper layer and lower layer metallic wiring films and select a resist-releasing agent incapable of corroding or deteriorating the upper and lower layer metallic wiring films. That is, there have been restrictions to the selection of etching agents or resist-releasing agents or ways to use them.